Enhanced regenerative braking control method for brake booster pressure build-up delay compensation

Abstract

A regenerative braking control method. An illustrative embodiment of the method includes selecting a vehicle speed at onset of transition from regenerative braking to friction braking of a vehicle, comparing the vehicle speed to a threshold value, applying a delayed regenerative braking torque ramp out to a hybrid powertrain and sending an undelayed regenerative braking torque ramp-out signal to a vehicle brake controller without at onset of transition from regenerative braking to friction braking of the vehicle if the vehicle speed falls below the threshold value.

What is claimed is: 
     
       1. A controller-implemented regenerative braking control method, comprising one or more controllers causing:
 applying a delay to a regenerative braking torque command from vehicle system controller to a hybrid powertrain, the delay following application of regenerative braking, the regenerative braking torque command comprising a delayed regenerative braking torque ramp-out signal initiating ramp-out (reduction) of regenerative braking force applied to the hybrid powertrain, the delay corresponding to a delay in applying a friction braking torque; 
 during the delay sending without the delay the regenerative braking torque command comprising an undelayed regenerative braking torque ramp-out signal to a vehicle brake controller at onset of transition from regenerative braking to friction braking of a vehicle if a speed of the vehicle falls below a threshold value; 
 calculating the friction braking torque by the vehicle brake controller using the undelayed regenerative braking torque command; and 
 applying the calculated friction braking torque while reducing the applied regenerative braking force. 
 
     
     
       2. The method of  claim 1  further comprising a step of comparing the vehicle speed to a threshold value, the threshold value corresponding to vehicle speed at initiation of regenerative braking torque ramp-out plus about 1 km/hr. 
     
     
       3. The method of  claim 2  further comprising a step of selecting a vehicle speed at onset of transition from regenerative braking to friction braking of a vehicle prior to said comparing the vehicle speed step. 
     
     
       4. The method of  claim 2  wherein the threshold value is about 9 km/hr. 
     
     
       5. The method of  claim 1  further comprising sending an estimated regenerative braking torque at wheel level signal to the vehicle brake controller if the vehicle speed is higher than the threshold value. 
     
     
       6. The method of  claim 1  wherein if the vehicle speed falls below the threshold value comprises if the vehicle speed falls between a pair of threshold values. 
     
     
       7. The method of  claim 6  wherein the pair of threshold values comprises a lower threshold value corresponding to the vehicle speed at initiation of regeneration torque ramp-out minus about 1 km/hr and an upper threshold value corresponding the vehicle speed at initiation of regeneration torque ramp-out plus about 1 km/hr. 
     
     
       8. The method of  claim 1  further comprising following the delay sending the delayed regenerative braking torque command to the hybrid powertrain if the vehicle speed falls between a pair of threshold values. 
     
     
       9. The method of  claim 1  further comprising sending an estimated regenerative braking torque at wheel level signal to the vehicle brake controller if the vehicle speed is lower than the threshold value. 
     
     
       10. A controller-implemented regenerative braking control method, comprising one or more controllers causing:
 selecting a vehicle speed at onset of friction braking of a vehicle; 
 comparing the vehicle speed to a threshold value; 
 transmitting a regenerative braking torque command from a vehicle system controller, the regenerative braking torque command initiating ramp-out (reduction) of regenerative braking force following the regenerative braking force being applied to a hybrid powertrain; 
 delaying sending of the regenerative braking torque command to the hybrid powertrain if the vehicle speed falls below the threshold value, the delay corresponding to a delay in applying a friction braking torque; 
 applying regenerative braking torque to the hybrid powertrain; and 
 during the delay sending without the delay the regenerative braking torque command comprising an undelayed regenerative braking torque ramp-out signal from the vehicle system controller to a vehicle brake controller at onset of friction braking of the vehicle if the vehicle speed falls below the threshold value; 
 calculating the friction braking torque by the vehicle brake controller using the undelayed regenerative braking torque command; and 
 applying the calculated friction braking torque while reducing the applied regenerative braking force. 
 
     
     
       11. The method of  claim 10  wherein the threshold value corresponds to the vehicle speed at initiation of regenerative braking torque ramp-out plus about 1 km/hr. 
     
     
       12. The method of  claim 11  wherein the threshold value is about 9 km/hr. 
     
     
       13. The method of  claim 10  wherein if the vehicle speed falls below the threshold value comprises if the vehicle speed falls between a pair of threshold values. 
     
     
       14. The method of  claim 13  wherein the pair of threshold values comprises a lower threshold value corresponding to the vehicle speed at initiation of regeneration torque ramp-out minus about 1 km/hr and an upper threshold value corresponding the vehicle speed at initiation of regeneration torque ramp-out plus about 1 km/hr. 
     
     
       15. A controller-implemented regenerative braking control method, comprising one or more controllers causing:
 selecting a vehicle speed at onset of friction braking of a vehicle; 
 comparing the vehicle speed to a threshold value; 
 transmitting a regenerative braking torque command from a vehicle system controller, the regenerative braking torque command initiating ramp-out (reduction) of regenerative braking force following the regenerative braking force being applied to the hybrid powertrain; 
 delaying transmission of the regenerative braking torque command to a hybrid powertrain if the vehicle speed falls below the threshold value, the delay corresponding to a delay in applying a friction braking torque; 
 during the delay sending without the delay the regenerative braking torque command comprising an undelayed regenerative braking torque ramp-out signal from the vehicle system controller to a vehicle brake controller at onset of friction braking of the vehicle if the vehicle speed falls below the threshold value; 
 sending an estimated regenerative braking torque at wheel level signal comprising the undelayed regenerative braking torque ramp-out signal to the vehicle brake controller if the vehicle speed does not fall below the threshold value; 
 calculating the friction braking torque by the vehicle brake controller using one of the undelayed regenerative braking torque command and the estimated regenerative braking torque; and 
 applying the calculated friction braking torque while reducing the applied regenerative braking force. 
 
     
     
       16. The method of  claim 15  wherein the threshold value corresponds to the vehicle speed at initiation of regenerative braking torque ramp-out plus about 1 km/hr. 
     
     
       17. The method of  claim 16  wherein the threshold value is about 9 km/hr. 
     
     
       18. The method of  claim 15  wherein if the vehicle speed falls below the threshold value comprises if the vehicle speed falls between a pair of threshold values. 
     
     
       19. The method of  claim 18  wherein the pair of threshold values comprises a lower threshold value corresponding to the vehicle speed at initiation of regeneration torque ramp-out minus about 1 km/hr and an upper threshold value corresponding the vehicle speed at initiation of regeneration torque ramp-out plus about 1 km/hr.